THE SKELETON AND TEETH 127
whom it tends to be square, with rounded angles. It differs from the oval form in the Orang, and the more circular outline in the Gibbons and Chimpanzee. Owen (374) regarded this feature as of considerable value for taxonomic purposes, as it does not appear to be an adaptive character. The inferior margin of the orbit is bevelled off, whereas it is sharper and more defined in the Chimpanzee. Within the orbit the lachrymo-ethmoidal suture is present in about a third of a large number of skulls, whereas a fronto-rnaxillary suture is present in two-thirds. The lachrymal hamulus is vestigial or absent. The infra-orbital canal is open from the commencement to the point where it passes through the maxilla on to the face; in the Chimpanzee it is bridged over to a variable extent. The infra-orbital foramen is relatively lower down than in the Chimpanzee, and is divided into two or more foramina by vertical bars of bone.
The inter-orbital width, is great, as in the Chimpanzee, being about the same size in both ; and it is larger in the male than in the female.
The nasal "bones are never less than 40 mm. long (Keith), and extend well below the inferior orbital margin, whereas they never exceed 25 mm. in the Chimpanzee. Their upper extremities pass into the interfrontal suture, whereas they do not in the Chimpanzee.
Some skulls have a median nasal crest The form of the conjoined nasal bones is shown in fig. 21, B ; and it will be seen on comparing it with those in figs, 21, c and 21, D that an approach to it is met with in some Chimpanzees, but in no Orang.
The nasal aperture varies in shape, being ovoid or